1. Field of Technology
The present invention relates to an AC generator apparatus for use in a motor vehicle, where the term “AC generator apparatus” is used in the following description to signify a generator apparatus driven by a vehicle engine, which generates an AC voltage and rectifies that AC voltage to derive an output DC voltage.
2. Description of Prior Art
A vehicle AC generator apparatus supplies electric power, as a rectified DC voltage, to the battery of the vehicle and to various electrical equipment, with the output voltage of the generator regulated to a predetermined value by a generator control apparatus. In general, the generator control apparatus (sometimes referred to as voltage regulator) adjusts an AC voltage produced by the generator by intermittently interrupting excitation current of an excitation winding (sometimes called the field coil) of the generator. Such a vehicle AC generator apparatus also is provided with a warning function whereby a charging warning lamp serves to indicate when the apparatus has started to perform normal generation, and so has started to supply a charging current to the vehicle battery. Such an AC generator apparatus is described for example in Japanese Patent Laid-open No. 10-225008 (pages 2–3, FIGS. 1–5).
With a generator control apparatus used in such a prior art type of vehicle AC generator apparatus, a phase voltage produced by the generator apparatus is smoothed by a smoothing capacitor, and the resultant voltage is inputted to a voltage comparator. When that voltage exceeds a predetermined value, the output from the comparator is applied to effect changeover of the charging warning lamp from the on (i.e., lit) condition to the off (i.e., extinguished) condition, to thereby notify the driver of the vehicle that normal generation by the AC generator apparatus has started. With such a generator control apparatus, if an excessive level of leakage current occurs in the rectifier elements (in general, rectifier diodes) of the AC generator apparatus, then while electrical generation is not being performed, that leakage current will flow through a resistor that is used to detect the phase voltage and hence will flow into the aforementioned smoothing capacitor. As a result, the charging warning lamp may remain in the off state after the vehicle ignition has been switched on but no electrical generation is being performed. Hence, the vehicle driver may be given an erroneous indication.
For that reason, it has been proposed in the prior art to provide a generator control apparatus incorporating a leakage compensation circuit, whereby the frequency of the phase voltage is detected, and whereby charging of the aforementioned smoothing capacitor is performed only when the frequency exceeds a predetermined threshold value. It is thereby possible to prevent the smoothing capacitor from being charged by leakage current that flows while electrical generation is halted, so that erroneous indications by the charging warning lamp can be prevented.
However, depending upon the forms of windings that are utilized, the AC generator apparatus may be of a first type, i.e., type A, whereby a high level of output current is produced when the frequency is within a high frequency range, or of a second type, i.e., type B, whereby a high level of output current is produced when the frequency is within a low frequency range. If a generator control apparatus is manufactured such that the aforementioned threshold value for detection of the frequency of the phase voltage is set at a high frequency fA that is suitable for an AC generator apparatus of type A, then it is possible that when that generator control apparatus is used with an AC generator apparatus that is of type B, the charging warning lamp will remain off even when the vehicle ignition is switched on but electrical generation is not occurring. Conversely, if the generator control apparatus is manufactured such that the threshold value used for detection of the frequency of the phase voltage is set at a low frequency fB that is suitable for an AC generator apparatus of type B, then it is possible that when the generator control apparatus is used with an AC generator apparatus that is of type A, the charging warning lamp will remain off even when the level of electric current that is being generated is insufficient to perform battery charging.
Hence, with such a prior art method, it is not possible to provide a single type of generator control apparatus that will be suitable for use with AC generator apparatuses that may be of type A or type B. It has thus been necessary to use a plurality of different types of generator control apparatus, incorporating respectively different types of leakage compensation circuits, in accordance with the specifications of various types of AC generator apparatus.
One method of detecting the phase voltage of such an AC generator apparatus irrespective of the frequency of that voltage is to detect the lowest frequency component of the phase voltage. However in order to detect a low frequency component it is necessary to use a circuit having a large time constant, so that the leakage compensation circuit will have a complex configuration, i.e., formed of capacitors, resistors, counters, etc. Thus, the overall scale of the generator control apparatus will become large. Moreover, when such a method is used, whereby the lowest frequency component is detected, the charging warning lamp will become turned off when engine cranking is occurring, during engine starting. On observing this, the vehicle driver may erroneously believe that engine starting has been achieved, and so halt the engine cranking operation before engine starting has actually occurred.